How to use heating and hot water systems efficiently

Heating, ventilation and air conditioning (HVAC) systems control the temperature, humidity and air quality in buildings, according to a set of chosen conditions. They do this by transferring heat and moisture in and out of the air and by controlling the level of air pollutants by directly removing them or by diluting them to acceptable levels.

HVAC systems vary widely in size and function. If they were designed and installed during the building's construction, they will be larger and a key component of the centralised building services. They will use ventilation to deliver both heating and cooling to the building.

Other systems provide heating through boilers and radiators, with some limited ventilation to provide fresh air or cooling to certain parts of the building.

In many buildings, individual comfort cooling units have been added to address a specific overheating problem that didn't exist originally or wasn't apparent at the time of the original design. For example, the huge increase in the use of computers, which generate a lot of heat, has meant that many older buildings now need additional cooling or ventilation. Comfort cooling units are the most common method of providing cooling to a building when the need arises.

Energy consumption of HVAC systems

There are five important factors that determine the energy use of an HVAC system. These are the:

• design, layout and operation of the building - this affects how the external environment impacts on internal temperatures and humidity
• required indoor temperature and air quality - more extreme temperatures, greater precision and more refined air quality are all factors which lead to the HVAC plant consuming more energy
• heat generated internally by lighting, equipment and people
• design and efficiency of the HVAC plant - which provides heat, cooling and moisture control exactly where it is needed in the building
• operating times of the HVAC equipment and functionality of the controls - these limit operation to exactly when the system is needed

One of the best ways to control the cost of using HVAC equipment is to reduce the need to use it initially. It's important to first take energy-saving measures such as insulation and draught-proofing around your building. Simple measures such as window blinds can reduce the amount of heat entering a building and reduce the need for cooling. Room or zone controls and thermostats allow people control over their immediate environment, although it may be necessary to reset controls to a default setting each day.

Other opportunities for saving energy include:

• the use of passive heating, ventilation and cooling
• night cooling - when cool air passes through a building overnight to remove heat that has built up through the day

Refurbishment and hardware opportunities

If you are refurbishing or putting in a new HVAC system it is worth using the most efficient system available.

The more efficient the HVAC system is, the less expensive it is to run, which is an important consideration as the day-to-day running costs are far greater than the initial costs of installation.

When choosing an HVAC system you should:

• choose the system that is best suited to your needs
• prioritise energy efficiency in the design and installation stages
• implement and maintain good system controls
• set up and maintain the system effectively and consider a maintenance contract